Method of and apparatus for continuously recovering and concentrating chemicals



July 5, 1932.

J. M. COAHRAN METHOD OF AND APPARATUS FOR CONTINUOUSLY RECOVERING ANDCONCENTRATING CHEMICALS Filed Aug. 19. 1927 2 Sheets-Sheet lfiaoiz'mzafin Column 52am)! Coils Steam Hails?" July 5, 1932. CQAHRAN1,865,887

METHOD OF AND APPARATUS FOR CONTINUOUSLY RECOVERING AND CONCENTRATINGCHEMICALS Filed Aug. 19. 1927 2 Sheets-Sheet 2 Patented July 5, 1932UNITED STATES PATENT OFFICE JESSE M. COAHRAN, OF SMETHPORT, PENNSYLVANIAMETHOD or AND APPARATUS roa oon'rmooosmr nnoovnnme AND ooncun'rm'rmeCHEMICALS Application filed August 19, 1927. Seria1 No. 214,189.

This invention relates to the recovery of chemicals, and while notrestricted to such use, has been developed with particular reference tothe recovery and partial purification of acetic acid from a solvent suchas ether by the use of which this acid in crude condition may have beenseparated from crude pyroligneous acid liquor.

The method-employed is applicable to the treatment of material which maybe separated by distillation into three portions of difierentvolatilities. The portion of greatest volatility is first distilled otlat a rela tively low temperature and the run-back comprising the othertwo portions is then distilled at a higher temperature to separate outthe second portion of intermediate volatility, leaving the third portionof lowest volatility as a residue. While the two distillations for anygiven quantity of the material are successively accomplished, accordingto the invention both are carried out simultaneously, the run-back fromthe first distillation being accumulated alternately in a pair of poolswhile the second distillation is carried on with the material of onepool while the other pool is being accumulate In the case of acetic acidrecovery from solvent such as ether containing it, the solvent is themost volatile constituent, the acetic acid is the major portion of theconstituent of intermediate volatility, and impurities such as tars,oils and certain acids, the constituents of lowest volatility.

One of the objects of this invention is to make possible the handling ofa maximum amount of material in a minimum amount of time with a minimumamount of apparatus and the minimum expenditure of heat.

A further object is to avoid any necessity for the pumping or flowing bygravity of liot corrosive chemicals between stills and storage,and toeliminate entirely any necessity for special storage apparatus'at anystage in the process. There is thus a substantial saving in initialcost, maintainance and replacement of apparatus.

These objects, as well as others which will hereafter appear, areattained by the use of two stills and two fractionating columns, one

column being used continuously to separate out and fractionate thesolvent, the other column being used continuously to fractionate thechemicals, and the twostills being used alternately, first to drive oflthe solvent into the solvent fractionating column and retain thechemical in heated condition, and then to vaporize the chemical byadditional heat into the chemical fractionating column. The separationof the solvent from the chemical is thus a batch process, being carriedon alternately in the two stills, while the solvent fractionation iscontinuous, the fractionation column drawing its supply from the stillscyclically, or in batch alternately from the two stills as will latermore fully appear.

For a more complete understanding of this invention, reference may behad to the accompanying drawings in which Figure 1 is a somewhatdiagrammatic perspective of the apparatus.

Figure 2 is a side elevation thereof;

Figure 3 is atop plan of the same.

Referring to these drawings, at'l and 2 are indicated respectively thesolvent and chemical fractionating columns. Beneath these are positionedthe stills 3 and 4. The solvent fractionating column 1 is connected bythe solvent vapor pipe5 with the solvent condenser 6. The chemicalfractionating column is connected by a similar vapor pipe 7 with achemical condenser 8. The mixture to be separated is supplied as throughthe pipe 10 to the fractionating column 1. The columns 1 and 2communicate through the return lines 12 and 13 with the end portions ofa pipe loop 14. The side portions of this pipe loop communicate as bythe riser pipes 15 and 16 with the stills 3 and 4, respectively. Thispipe.

loop thus forms the lower portion of a trap between the columns andstills. Valves 17 and 18 control communication from the return line 12,and similar valves 19 and 20 control communication from the return line13 to these stills, communication from both return lines being madethrough the riser pipes 15 and 16 to the respective stills. Sim-' ilarlyboth columns 1 and 2 communicate'with the upper portion of each of thestills, as

alternately. The chemical column operates through the pipes 25 and 26,communication between the column 1 and the still 3 being controlled bythe valve 27, communication between the column 1 and the still 4 by thevalve 28, communication between the column 2 and the still 3 by thevalve 29, and communication between the column 2 and the still 4 by thevalve 30. The stills may be heated by any suitable means, as hereinshown steam inlet and outlet pipes 35 and 36 being provided to supplysteam coils in the stills.

In operation the mixture to be separated is introduced through the pipe10 into the column 1, the descending liquids being met by the hot vaporsrising from one of the stills, either 3 or 4, dependmg on the conditionsof the controlling valves. Assuming, for example, that the valves 17,20, 27 and 30 are open and the valves 18, 19, 29 and 28 are closed, thehot vapors arise from the still 3 and meet the down-coming liquids inthe column 1, the heat causing the solvent to be driven off in thecolumn 1 through the vapor pipe and into the solvent condenser 6 fromwhich it may be removed to the solvent storage. The less volatileconstituents of the mixture, in the case of acetic acid and solvent thiscomprising the acetic acid together with impurities such as propionicand butyric acids, methanol, aldehydes, phenols, oils, and tars, andsome water, pass down through the return pipe 12 into the still 3. Thiscontinues until the still 3 is substantially full of the crude impureacid. When the still 3 has been so supplied with a pool of thismaterial, the valves 17,20, 27 and 30 are closed, and valves 18, 19, 28and 29 are opened, whereupon the column 1 receives the hot vapor supplyfrom the still 4 and the acid passing down through the pipe 12 passesinto the still 4. The still 3 which has thus been filled with acid andwhich is hot is then still further heated as by means of the steamcoils, the vapor passing up through the pipe 25 past the open valve 29and into the chemical fractionating column 2 where it is driven ofithrough the pipe 7 and condensed in the condenser 8.

The constituents of the crude acid come oil from the column 2 in aboutthe following order: (1) Ether containing a very small percentage ofacid. This is returned to the extractor by which the crude acetic acidwas separated from the pyroligneous acid liquor, with the feed liquor.(2) Light and then heavy wood oils with very little acid which isdisposed of as oil. (3) Water containing increasingly larger amounts ofacid, some acetic but more propionic and butyric. (4) Acid increasing instrength from 15% to 98% and containing also some water and somepropionic and butyric acid. The weaker portion of this is returned tothe still which is being filled with crude acid, the return beingconnected to the trap coil 14 as shown at 40 in Figure 3, the strongerportion being collected uids are collected alternately in one of twopools from which they are distilled into the other fractionating columnwhere they are partially separated, concentrated, and recovered, the onepool being accumulated from the first fractionating column while theother is being used to feed the second fractionating column.

It will thus be seen that no pumping or 'gravity feed of hot corrosiveliquids from or to storage receptacles is necessary and that no separatestorage receptacle other than the stills by which the vaporization iseffected is necessary, and that the heat content of the less volatileliquid as it passes from the first column is utilized to its full extentwhen it is subjected to distillation and fractionation.

From the foregoing description of an embodiment of thisinvention itshould be evident to those skilled in the art that various changes andmodifications might be made therein without departing from the spirit orscope of the invention as defined by the appended claims.

I claim:

1. The process which comprises continuously fractionating a mixture ofcrude acetic acid containing impurities less volatile than the acid andan acetic acid solvent more volatile than said acid so as to remove saidsolvent, collecting the crude acid containing said impuritiesalternately in a pair of pools, and distilling and fractionating thecrude acid alternately from each one of said pools 'so as to separateout acetic acid from said one 001 while the other pool is beingaccumulated? 2. The process of treatin a liquid mixture havingconstituents of di erent volatilities, which comprises continuouslysupplying the mixture to a fractionating zone and removing theconstituents of highest volatility, reflexing the remaining constituentsalternately in a pair of differentially heated pools, and vaporizingconstituents from one of said pools at a higher temperature than forremoval of the constituents of highest volatility in the fractionatingzone and removing therefrom the constituents of intermediate volatility,while the other pool is being accumulated.

3. An apparatus comprising a air of fractionating columns of substantialy identical capacity, a pair of stills, means for supplying a mixtureof three constituents of different volatility to be separated to one ofsaid 001- umns to drive off and recover the most vola- ,tileconstituent, means to convey the two less volatile constituents of saidmixture at will to either of said stills while said still supplies vaporto said one column, and means for distilling from the still notreceiving flow at any time to the other of said columns to drive off andrecover the constituent of intermediate volatility while leaving theconstituent of least volatility.

4. An apparatus of the class described, comprising a pair offractionating columns of substantially identical capacity, a pair ofstills below said columns, heating means in each still, means forsupplying liquid to one of said columns, and valved connections betweensaid columns and still for directing hot vapor from either selectedstill to either selected one of said columns and to return the run-backfrom said one column to said selected still, and simultaneouslytherewith to direct the vapor distilled from the other of said stills tothe other of said columns.

5. An apparatus of the class described comprising a pair offractionating columns, a pair of stills below said columns, heatingmeans in each still, means for supplying liquid to one of said columns,valved'connections between said columns and stills for directing vapordistilled from either selected still into either selected column, andvalved connections independent of said vapor connections and havingtraps therein between said columns and stills for directing the runbackfrom either of said columns selectively into either of said stills.

In testimony whereof I have afiixed my signature.

JESS-E M. COAHRAN.

